The present invention relates to a structure of an anode of a magnetron suitable for use in a microwave heating apparatus and to a method of manufacturing a magnetron having this structure.
A method of manufacturing the anode of a magnetron by a hobbing working method has been disclosed in U.S. Pat. No. 3,678,575 (invented by Akeyama et al) filed on July 25, 1972 which is assigned to the same assignee of the present invention. This method includes the process of removing the remaining portion by the cutting work after the hobbing work.
In the anode of a magnetron, a plurality of vanes constituting a resonator are formed in the inside of a cylindrical outer frame. Methods for adhering the vanes to the outer frame by soldering has are known. There is a problem in such methods in that in mass production a large amount of expensive silver solder is needed, the soldering process is necessary and the like. Therefore, it is desirable to simultaneously integrally manufacture the outer frame and the vanes by hobbing working a material.
As another anode structure and a method of manufacturing the same, for example, there is known an anode with such a structure that after an anode was divided into two parts and manufactured, both of them are adhered by soldering as disclosed in JP-A 48-58764 on the basis on the invention applied to Japanese Patent Office by Hitachi, Ltd. on Aug. 17, 1971. In addition, a method of manufacturing an anode by the hobbing working has been disclosed in JP-A No. 52-24070 based on the invention applied to Japanese Patent Office by Toshiba Corporation on Aug. 19, 1975. According to this method, a disk-shaped portion is left in the central portion of a cylinder, vanes are formed integrally with the cylindrical outer frame by hobbing, and the remaining disk-shaped portion is finally struck by pressing.
The fundamental oscillating frequency of the magnetron for microwave heating is strictly regulated by the law and it is required that unnecessary spurious radiation be prevented. Therefore, high dimensional accuracy of the anode as a resonator is required. To meet this requirement, copper, in particular, oxygen-free copper is generally used as a material of the anode since it is a non-magnetic material and it is easy to work. Although copper can be easily worked, it is weak and easily deformed by a mechanical stress. For example, although the anode is used with radiator fins for cooling arranged to the outside of the anode, when the fins are pressure inserted into the outside of the anode, the anode is deformed, creating the possibility that the oscillating frequency, operating voltage, and efficiency may deviate from the desired design values. Also, unnecessary harmonic components are generated and radiated due to the deformation. Further, while the magnetron is being used, the temperature of the central portion of the anode becomes high but the temperature of the outside of the anode is low because it is cooled, causing the anode to be subjected to a thermal stress which causes deformation. Such a deformation causes deformation of a strap ring which is used for adjusting the oscillating frequency of the magnetron upon manufacturing. In the worst case, the function of the anode is lost.
Therefore, it is desirable that the anode of the magnetron have a structure which is suitable for mass production which does not include the soldering and cutting works and also has an excellent mechanical strength.